Higher order taxa

Species

Description and significance

Like the other members of the Lactobacillus genus,
Lactobacillus gasseri is an anaerobic, gram-positive bacterium that falls into the category of lactic acid bacteria. It is also a rod shaped and of the non-spore-forming type. It is typically found in the gastrointestinal tracts of humans and animals due to its largely fermentative function (1,2,3). Although mainly in the GI tract, it can also be found in many other places as well (see Ecology).

Isolation of this bacterium was achieved by taking a sample from the gastrointestinal tract and was discovered to be part of the lactobacillus acidophilus complex (4).

This bacterium is very important to many applications in daily life. One of its roles, as described above, is fermentation in the GI tract. Recently, its function as a probiotic has been the area of most interest (1).

Genome structure

The complete genome has been sequenced by a combination of efforts from Joint Genome Institute, Fidelity Systems Inc., and North Carolina State University. The final draft was accepted on October 13, 2006. Lactobacillus gasseri ATCC 33323 was the strain they used to come up with the sequence (5). (ATCC stands for American Type Culture Collection)

The genome is circular and contains 1.894362 Mb (5). The GC content of the sequence was found to be 35.3% which makes the AT content to be 64.7%. There were also 1755 different proteins identified as well as 98 different RNAs present (6).

The mapping of the sequence gives great information about the role and function of this bacterium. Dr. Todd Klaenhammer states “L. gasseri is substantially more amenable to DNA introduction and manipulation which has lead to the development of more genetic tools that will be useful in the functional genomic analysis of this species” (5).

Cell structure and metabolism

Lactobacillus gasseri is rod shaped and a gram-positive bacterium. This implies that it has a very thick outer cell wall. It is also classified as a non-spore-forming type. One feature that is still being researched is how this adheres to intestinal cells. It was determined that “mannose-specific proteinaceous adhesion” is responsible for L. gasseri’s ability to attach to the intestinal linings when the mucosal layer is encountered (7). Another interesting feature is the use of Aggregation-promoting factor (APF) to create and support the rod shape. The APF protein was examined and the researchers concluded that it truly did alter the cell shape based on its amount present in the cell (8).

L. gasseri is an anaerobe so it lives mostly in regions where no oxygen is present. It also participates in fermentative actions which produce lactic acid as well as the energy required for growth. One other interesting thing that is made by this bacterium is hydrogen peroxide which is found in the vaginal tract. Research was done with cattle to examine the effectiveness of this hydrogen peroxide producing bacteria as a probiotic (9). (See Current Research)

Ecology

Even though this bacterium is most commonly found in the gastrointestinal tract, it can also be found in various other places.

One very important location is in the vaginal tract of reproductive, normal women. Its role is to protect the vagina from infections (10). This correlates with the hydrogen peroxide produced, as described in the Cell Structure and Metabolism section.

It is can also be found in the fecal waste products of adult humans as well as in the mucosa layer of the rectum and oral cavity. With L. gasseri heavily found in humans and animals, a significant amount of research has been conducted to try and find out exactly what this bacterium and its fellow genus members actually do as well as how it can operate as a probiotic (10).

Pathology

In 2004, Lactobacillus gasseri was identified as a cause of Fournier's gangrene (11). Fournier's gangrene is a “bacterial infection of the skin that affects the genitals and perineum”. It is most typically due to a wound that is infected on the skin between the genitals and the anus. Some typical symptoms include soft, spongy skin, discolored skin, pus, genital pain, and an odor (12).

Application to Biotechnology

Lactobacillus gasseri as well as the rest of the lactobacillus genus are known for their role in fermentation of many different food products. One example is the use of lactobacillus gasseri in fermenting meat. Many of the lactic acid bacteria are useful for this type of process, but L. gasseri was found to be the most dominant in the human gut. With this being said, it will provide less complications in the digestive system which makes it the best choice to ferment the meat. This bacterium will not only decrease the ability of pathogens like Staphylococcus aureus to grow in the meat, but would also function as a probiotic for the intestinal flora of the human GI tract. This would produce a much healthier meat product for all to consume (13).

Current Research

The use of antibiotics in dairy farms to keep the cattle healthy from reproductive problems has left residues in the food products obtained. Also an increased resistance to these drugs has been observed as well as increased costs of supplying these drugs. Lactobacillus gasseri is found in the vaginal tract. Research was conducted on the amount of hydrogen peroxide two strains (CRL1421 and CRL141) generated in different conditions. Also the interaction with Staphylococcus aureus was looked at in the cultures. It was observed that the lactic acid and the hydrogen peroxide had a very strong effect on the pathogen. S. aureus had “a different type of morphological damage” from the lactic acid and hydrogen peroxide. This concluded that lactobacillus gasseri could be used as a probiotic to help combat the infections seen in cattle.

Oxalate can cause many problems in the human body including excess urinary oxalate and cause kidney stones to form. This compound is introduced to the body by plants that are eaten. Lactobacillus gasseri has formyl coenzyme A transferase (frc) and oxalyl coenzyme A decarboxylase (oxc) on its genome which may have a role in oxalate degradation. Research found that L. gasseri does in fact break down oxalate in vitro. To test this finding in vivo the bacteria was cultured in human fecal matter to simulate colon conditions. It was found that oxalate degradation occurred in the section which corresponded to the proximal colon. These findings give some insight on using L. gasseri as a possible treatment for those with kidney stones.

Allergic disease due to enhanced immunoglobulin E (IgE) responses to common stimuli has become more common in the population. The internal microbiota has been identified to play a part in regulating the immune function in humans. Due to this observation, an experiment was setup with 15 people that showed the enhanced IgE responses. These subjects drank milk fermented with Lactobacillus gasseri TMC0356 and were observed. The results were that the levels of the IgE were decreased. This data shows that IgE was reduced, but no data was found on whether allergic responses were reduced as well. A promising future is ahead of this type of fermented milk, but further research on the effects on the person must be conducted to see if this is a safe way to go.